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. 2010 Mar 10;91(5):1324–1335. doi: 10.3945/ajcn.2009.28908

TABLE 1.

Mean serum 25-hydroxyvitamin D [25(OH)D] concentrations by potential predictors of serum 25(OH)D status with and without adjustment for month of blood draw: sample from the nested case-control studies of the Women's Health Initiative Calcium plus Vitamin D Clinical Trial (n = 3055)1

25(OH)D Concentration
Characteristic No. of subjects Unadjusted Adjusted for month of blood draw2
mmol/L
Serum 25(OH)D
 Quintile 1: 6.3–30.2 nmol/L 616 21.5 ± 0.243 21.5 ± 0.32
 Quintile 2: 30.4–40.6 nmol/L 598 35.8 ± 0.12 35.9 ± 0.32
 Quintile 3: 40.9–51.4 nmol/L 615 45.9 ± 0.12 45.9 ± 0.32
 Quintile 4: 51.6–66.8 nmol/L 620 58.5 ± 0.18 58.5 ± 0.32
 Quintile 5: 67.1–156.6 nmol/L 606 84.7 ± 0.63 84.7 ± 0.32
 P value4 <0.001 <0.001
Estimates of sunlight exposure
 Regional estimate
  Latitude of clinic center °N
   Northern: >40 °N 1473 48.7 ± 0.58 48.6 ± 0.59
   Middle: >37–40 °N 651 49.0 ± 0.90 49.2 ± 0.88
   Southern: ≤37 °N 931 50.3 ± 0.77 50.4 ± 0.74
   P value4 0.094 0.062
  Langleys of clinical center
   Quintile 1: 300–325 g-cal/cm2 936 49.0 ± 0.74 49.1 ± 0.73
   Quintile 2: 350 g-cal/cm2 726 48.8 ± 0.82 48.4 ± 0.84
   Quintile 3: 375–380 g-cal/cm2 304 47.9 ± 1.31 47.7 ± 1.29
   Quintile 4: 400–430 g-cal/cm2 507 46.6 ± 0.97 47.0 ± 1.00
   Quintile 5: 475–500 g-cal/cm2 582 53.3 ± 1.01 53.5 ± 0.93
   P value4 0.031 0.014
  Watts of clinical center
   Quintile 1: 0.4–0.5 (J/s)/m2 718 48.4 ± 0.85 48.3 ± 0.84
   Quintile 2: 0.7 (J/s)/m2 742 49.3 ± 0.80 49.0 ± 0.83
   Quintile 3: 1.0 (J/s)/m2 559 48.5 ± 0.96 48.5 ± 0.95
   Quintile 4: 1.4 (J/s)/m2 677 49.8 ± 0.90 50.2 ± 0.87
   Quintile 5: 1.5–1.9 (J/s)/m2 359 51.3 ± 1.28 51.3 ± 1.19
 P value4 0.073 0.026
 Individual estimates
  Total time spent walking each week5
   0 h 1031 46.8 ± 0.70 47.0 ± 0.70
   0 to <1 h 453 47.5 ± 1.08 47.5 ± 1.05
   ≥1 to <2 h 539 50.3 ± 0.98 50.2 ± 0.96
   ≥2 h 727 51.6 ± 0.83 51.5 ± 0.83
   P value4 <0.001 <0.001
Sources of vitamin D from diet and supplements
 Vitamin D intake from foods, energy-adjusted5
  Quintile 1: 0.12–2.35 μg/d 601 44.3 ± 0.96 44.5 ± 0.92
  Quintile 2: 2.36–3.23 μg/d 565 48.5 ± 0.97 48.3 ± 0.94
  Quintile 3: 3.23–4.17 μg/d 573 48.9 ± 0.91 49.0 ± 0.94
  Quintile 4: 4.18–5.69 μg/d 576 52.3 ± 0.97 52.2 ± 0.93
  Quintile 5: 5.69–26.27 μg/d 589 54.0 ± 0.91 53.9 ± 0.92
  P value4 <0.001 <0.001
 Vitamin D intake from supplements5
  None 1598 44.0 ± 0.55 43.9 ± 0.54
  ≤10 μg/d 1124 53.7 ± 0.65 53.8 ± 0.65
  >10 μg/d 291 61.0 ± 1.38 61.4 ± 1.28
  P value <0.001 <0.001
 Vitamin D intake from foods and supplements, energy-adjusted5
  Quintile 1: 0.09–3.10 μg/d 596 40.9 ± 0.93 40.8 ± 0.90
  Quintile 2: 3.10–5.28 μg/d 567 45.8 ± 0.93 45.8 ± 0.92
  Quintile 3: 5.29–10.40 μg/d 569 50.1 ± 0.95 50.0 ± 0.92
  Quintile 4: 10.40–14.94 μg/d 554 53.3 ± 0.88 53.5 ± 0.93
  Quintile 5: 14.96–78.77 μg/d 579 58.1 ± 0.95 58.2 ± 0.91
  P value4 <0.001 <0.001
Potential modifiers of vitamin D synthesis from sunlight exposure
 Age at baseline screening
  50–54 y 268 48.9 ± 1.53 48.7 ± 1.38
  55–59 y 555 50.2 ± 0.96 49.9 ± 0.96
  60–64 y 632 49.9 ± 0.91 49.8 ± 0.90
  65–69 y 740 49.9 ± 0.84 50.0 ± 0.83
  70–74 y 577 49.1 ± 0.92 49.3 ± 0.94
  75–79 y 283 45.1 ± 1.37 45.3 ± 1.34
  P value4 0.051 0.114
 Race-ethnicity
  White 2726 50.4 ± 0.44 50.4 ± 0.43
  African American 164 34.8 ± 1.32 35.1 ± 1.74
  Hispanic 76 41.2 ± 2.47 40.1 ± 2.56
  American Indian 11 42.0 ± 6.92 41.3 ± 6.71
  Asian/Pacific Islander 51 47.9 ± 3.35 49.0 ± 3.12
  Unknown 27 49.9 ± 4.85 50.4 ± 4.28
  P value4 <0.001 <0.001
Anthropometric characteristics that may modify vitamin D status
 Weight
  Quintile 1: 41.2–61.8 kg 610 57.1 ± 1.04 56.9 ± 0.89
  Quintile 2: 61.9–68.8 kg 612 52.0 ± 0.90 51.9 ± 0.89
  Quintile 3: 68.9–76.4 kg 608 47.9 ± 0.90 48.4 ± 0.90
  Quintile 4: 76.5–86.0 kg 616 46.2 ± 0.84 46.0 ± 0.89
  Quintile 5: 86.1–190.0 kg 609 43.2 ± 0.82 43.2 ± 0.89
  P value4 <0.001 <0.001
 Waist circumference5
  Quintile 1: 56.4–76.4 cm 604 58.4 ± 1.01 58.2 ± 0.89
  Quintile 2: 76.5–83.5 cm 617 51.8 ± 0.94 51.9 ± 0.88
  Quintile 3: 83.6–90.2 cm 604 47.0 ± 0.90 47.1 ± 0.89
  Quintile 4: 90.5–99.5 cm 623 46.2 ± 0.83 46.3 ± 0.88
  Quintile 5: 99.8–158.9 cm 606 43.0 ± 0.81 42.9 ± 0.89
  P value4 <0.001 <0.001
 Waist-to-hip ratio5
  Quintile 1: 0.43–0.76 610 54.8 ± 0.97 54.8 ± 0.91
  Quintile 2: 0.76–0.80 610 51.2 ± 0.95 51.3 ± 0.90
  Quintile 3: 0.80–0.83 612 48.1 ± 0.88 48.0 ± 0.90
  Quintile 4: 0.83–0.88 611 46.4 ± 0.91 46.4 ± 0.90
  Quintile 5: 0.88–2.58 611 45.9 ± 0.87 45.9 ± 0.90
  P value4 <0.001 <0.001
 BMI5
  Quintile 1: 15.8–23.8 kg/m2 609 58.0 ± 1.04 58.1 ± 0.89
  Quintile 2: 23.8–26.3 kg/m2 610 52.8 ± 0.88 52.5 ± 0.89
  Quintile 3: 26.4–29.1 kg/m2 610 47.2 ± 0.92 47.5 ± 0.89
  Quintile 4: 29.1–32.7 kg/m2 610 45.5 ± 0.84 45.6 ± 0.89
  Quintile 5: 32.7–69.3 kg/m2 610 42.8 ± 0.80 42.7 ± 0.89
  P value4 <0.001 <0.001
Other health and lifestyle characteristics
 Education5
  0–8 y 25 42.4 ± 4.24 42.7 ± 4.50
  Some high school 117 43.6 ± 2.01 43.0 ± 2.08
  High school diploma/GED 599 49.8 ± 0.99 49.7 ± 0.92
  School after high school 1182 48.6 ± 0.66 48.8 ± 0.66
  College degree or higher 1116 50.5 ± 0.68 50.4 ± 0.67
  P value4 0.011 0.008
  Recreational physical activity5
  Quintile 1: 0–0.5 MET-h/wk 532 44.3 ± 0.90 44.6 ± 0.96
  Quintile 2: 0.75–4.50 MET-h/wk 578 45.5 ± 0.91 45.5 ± 0.92
  Quintile 3: 4.54–9.50 MET-h/wk 528 49.6 ± 0.99 49.2 ± 0.96
  Quintile 4: 9.58–17.42 MET-h/wk 541 50.0 ± 0.98 50.1 ± 0.95
  Quintile 5: 17.50–113.17 MET-h/wk 552 55.9 ± 1.00 55.8 ± 0.94
  P value4 <0.001 <0.001
 Smoking status5
  Never smoked 1584 49.1 ± 0.56 49.0 ± 0.57
  Past smoker 1213 50.2 ± 0.66 50.2 ± 0.65
  Current smoker 222 46.6 ± 1.70 46.5 ± 1.51
P value4 0.074 0.058
 History of osteoporosis56
  No 2773 49.3 ± 0.43 49.3 ± 0.43
  Yes 231 49.6 ± 1.56 49.5 ± 1.49
  P value4 0.850 0.923
 History of diabetes56
  No 2905 49.7 ± 0.43 49.7 ± 0.42
  Yes 148 41.8 ± 1.61 41.5 ± 1.85
P value4 <0.001 <0.001
 Medication use7
  Hormone therapy use
   None 1047 47.0 ± 0.67 47.0 ± 0.69
   Past 469 49.0 ± 1.09 49.1 ± 1.04
   Current estrogen alone 699 49.9 ± 0.88 49.9 ± 0.85
   Current estrogen + progesterone 840 51.7 ± 0.80 51.7 ± 0.78
   P value4 <0.001 <0.001
  Osteoporosis-related medication use8
   No 2992 49.1 ± 0.42 49.2 ± 0.41
   Yes 63 55.2 ± 2.98 55.1 ± 2.84
   P value4 0.038 0.038
  Antihypertensive medication use
   No 2680 49.8 ± 0.44 49.7 ± 0.43
   Yes 375 45.8 ± 1.16 45.9 ± 1.16
   P value4 0.002 0.002
1

Quintile ranges appear to overlap because differences in values between quintiles occur at the third decimal place and are not shown in this table. MET-h, metabolic equivalent task hours; GED, general equivalent diploma.

2

To adjust for month of blood draw, serum 25(OH)D concentrations were regressed on month of blood draw to compute residuals, which were added back to the mean serum 25(OH)D concentration in the sample.

3

Mean ± SE (all such values).

4

P values were derived from generalized linear models to estimate least-squares means of serum 25(OH)D, adjusted for month of blood draw, by level of noted characteristic.

5

Total n does not add up to 3055 because of missing data.

6

Reported at baseline or during follow-up but before year 1 blood draw.

7

No statistically significant differences (P < 0.05) by concentration of 25(OH)D were observed for use of the following medications: anticonvulsants, hematopoietic agents, anticoagulants, steroids/corticosteroids, antihyperlipidemic agents, or statins (data not shown).

8

Reported osteoporosis-related medications were alendronate, salmon calcitonin, raloxifene, and etidronate.